Precision ball screw units are invaluable in manufacturing. The motion they impart along the axis of the screw must be precise and controllable. Naturally, after a passage of time in use, the ball bearings and/or the raceways for them wear, which reduces the precision and control of the unit from that which is imparted by the ball bearings and their races being under an appropriate tension to a point where the tension is lessened, which may even be to the point where the screw turns freely in the nut, a condition called “backlash.” A precision ball screw unit with backlash is no longer a precision unit, for instance, having devolved from a machine for manufacturing precision parts to that for roughing in or making crude parts only.
Repair of a machine having a compromised precision ball screw unit can be an enormous problem. It is common to take one to four days in the field to remove the compromised ball screw unit and ship it to a repair facility, two to three week under normal conditions to repair and reload the unit at the facility, including wait time in the queue, and ship the repaired unit, and another day or two back in the field to reinstall and qualify the repaired unit. In addition, when a backlash condition occurs and repair of the precision ball screw unit is sought, since the condition is symptomatic of fairly extensive wear, not uncommonly other things are found in need of repair in the unit, increasing the expense and repair time even further. The total time for major repair and reinstallation could reach six to eight weeks. Of course, back in the field, the manufacturing down time, labor expense, and loss of revenues can be great and extensive, if not debilitating.
Many nuts for precision ball screw units are of the double nut variety.
Various attempts at adjusting a worn double nut ball screw unit are known. Among these are those that employ a threaded, rotatable spacer between the two major pieces of the double nut, which themselves are correspondingly threaded, which spacer is rotated to change the position of the races in the nuts relative one another to provide tension for the ball bearings. This design is known as an Adjust-o-Lok® ball screw and nut assembly, and its rotating spacer is located on the major diameter of the ball nut assembly, which is not easily accessible. Such a design is for rolled thread type ball screws, not precision ball screws. In any event, in such a design and others, the worn ball screw unit still must be removed from its mount in the machine to make the adjustment, and then be reinstalled and, as may be applicable, qualified, which may take a significant amount of time, which engenders significant manufacturing down time and its expenses and loss or revenue. See also, U.S. Pat. Nos. 3,124,969 and 4,487,087. A hydraulic self adjusting ball screw is known. It, too, provides for application of axially directed force, and it is very expensive.
Further art is known. See, e.g., U.S. Pat. Nos. 3,059,494; 3,498,651; 4,008,625; 4,463,041; 4,669,324; 4,827,789; 5,193,409; 5,501,118; 5,467,661; 5,582,072; 5,697,252; 5,911,789; 6,082,209; 6,142,032; and U.S. Pat. No. 6,928,895 B2; U.S. Pat. No. 7,337,688 B2; U.S. Pat. No. 7,506,557 B2 and U.S. Pat. No. 7,562,596 B2.
As well, particulate waste from manufacturing can quickly erode a ball screw.
Furthermore, as set forth in the Ser. No. 12/924,503 regular utility application, among types of ball screw nuts further to tube ball-return types may be mentioned 20th Century, Flopover, Starr, Cincinnati, and Jena-Tec models. Such nuts can have high unit and installation costs, a lack of adaptability to various ball screws or machinery therewith, a quick rate of wearing out and/or a practical inability or economic un-viability to repair some models. Compare, U.S. Pat. Nos. 477,642; 611,832; 1,704,031; 2,380,662; 3,053,105; 4,638,548; 4,760,635; 4,953,419; 5,063,809; 5,493,929; 5,653,145; 5,791,192; and patent or publication Nos. U.S. Pat. No. 6,176,149 B1, U.S. Pat. No. 6,425,302 B2, U.S. Pat. No. 6,446,520 B1, US 2006/0137485 A1, US 2007/0186708 A1, U.S. Pat. No. 7,516,681 B2, U.S. Pat. No. 7,520,193 B2, U.S. Pat. No. 7,523,681 B2 and U.S. Pat. No. 7,523,682 B2—of which those to Chen, Lee, Misu, Greubel and Pan et al. may be of greater possible interest in this connection.
It would be desirable to more effectively address and/or ameliorate if not solve one or more of such problems. It would be desirable to provide the art an alternative.